There are many known types of welding-type power supplies. Welding-type power, as used herein, refers to power suitable for welding, plasma cutting, induction heating, CAC-A and/or hot wire welding/preheating (including laser welding and laser cladding). Welding-type systems are often used in a variety of applications and often include an auxiliary output to mimic utility power for powering tools, lights, etc. Welding-type system, as used herein, is a system that can provide welding type power, and can include control and power circuitry, wire feeders, and ancillary equipment. Utility power, as used herein, is power provided at a voltage and frequency by an electric utility.
Welding-type systems are often used in a variety of applications and often are used at sites where utility power is not available or insufficient. In such applications welding type systems include, or receive power from, an engine driven generator. Engine driven generators that are part of welding type systems often attempt to mimic utility power because the welding type power supply portion of the system is often designed to be used with either utility or engine power. Also, such systems typically provide an auxiliary output for tools etc.
One prior art welding power supply that is well suited for portability and for receiving different input voltages is a multi-stage system with a preregulator to condition the input power and provide a stable bus, and an output circuit that converts or transforms the stable bus to a welding-type output. Examples of such welding-type systems are described in U.S. Pat. No. 7,049,546 (Thommes) and U.S. Pat. No. 6,987,242 (Geissler), and US Patent Publication 20090230941 (Vogel), all three of which are owned by the owner of this invention, and hereby incorporate by reference. Miller® welders with the Autoline® feature include some of the features of this prior art.
Providing welding-type power, and designing systems to provide welding type power, provides for some unique challenges. For example, power supplies that are not designed for welding-type outputs are typically designed for relatively steady loads. Welding, on the other hand, is a very dynamic process and numerous variables affect output current and load, such as arc length, electrode type, shield type, air currents, dirt on the work piece, puddle size, weld orientation, operator technique, and the type of welding process determined to be most suitable for the application. These variables constantly change, and lead to a constantly changing and unpredictable output current and voltage. Moreover, welding type systems should provide auxiliary power at a constant and steady voltage, to properly mimic utility power. Finally, power supplies for many fields are designed for low-power outputs. Welding-type power supplies are high power and present many problems, such as switching losses, line losses, heat damage, inductive losses, and the creation of electromagnetic interference. Accordingly, welding-type power supply designers face many unique challenges.
Welding-type systems with engine driven generators also face the challenges above. The prior art typically used conventional engine driven generators that were not designed to address the problems unique to welding type systems. Accordingly, such prior art welding type systems had generators that were capable of providing the peak power needed for welding. When welding was being performed the engines operated at a run speed. When welding was not being performed the engines idled. When the engine was running at run speed and welding at less than the maximum output was being performed, energy was being wasted. Thus, these prior art systems were inefficient, especially when running at full speed for less than the maximum output.
Given the dynamic load of welding, it is challenging to match the power generated to the power consumed by the welding and auxiliary operations. The speed of the engine in welding systems has been controlled in response to the load, and one such system is shown in U.S. Pat. No. 5,698,385, entitled ENGINE DRIVEN INVERTER WELDING POWER SUPPLY, issued to Beeson et al. These systems were a significant advance over the prior art, because the engine could run faster (and produce more power) when needed. Prior art systems typically used separate stators for welding an auxiliary power, and as such were relatively complex and expensive.
However, the load can change much faster than the engine speed can change. Thus, it can be difficult for the system to compensate for load changes by simply controlling engine speed. Prior art systems needed to be able to quickly provide the maximum power, so they often ran at speeds capable of producing more power than was needed. Also, as the speed changed, particularly as the speed was decreasing, power was wasted.
Much of the prior art accommodated the unique needs of welding with designs that provided the peak power needed by welding. However, constantly running a generator to provide its peak output means the system is outputting more power than needed. The engine is running faster, and more fuel is being consumed. Some systems used multiple speeds, such as run and idle, so that the peak is provided only at certain times. But, given the nature of welding, this still results in periods where the engine is running faster than necessary, or worse, when the engine and system fail to provide the needed power.
Welding processes are often started using a hot start, where additional output power is provided to start welding. The engine might produce enough power at the idle speed for steady state welding, but the additional power needed for a hot start is not available at idle. Thus, the engine speed must be increased to run to provide the power for the hot start. For example, some prior art engine driven welding-type systems idle at 1800 RPM and run at 3600 RPM. Assuming, the user select a nominal steady state output current of 150 A, and a nominal arc voltage of 26V for welding with a ⅛″ 7018 stick electrode, a prior art system could provide the power to weld at 150 A at an idle speed of 1800 RPM. But a hot start might require an additional 150 A (for a total of about 300 A for a duration of about 150 msec (the hot start time), which is more than the power available at idle speed. Thus, prior art systems would increase to the run speed to perform the hot start—even though the hot start is for a relatively short duration.
Accordingly, an engine driven welding type system is desired that more efficiently produces the energy needed for the welding and auxiliary operations. Preferably, such as system runs at a desired speed, and has energy storage to temporarily absorb or provide energy to the weld when the weld power demand changes faster than the power provided by the engine/generator can be changed.